The Cysteamine Study provided answers to the question of the drug's efficacy with some inferential difficulty, since cysteamine's unpleasant taste and smell rendered it unpalatable to many patients, who subsequently did not receive effective amounts of the drug. The design of the study itself, with no randomized concurrent control group, obscured effects and required a good deal of reliance on adjustment techniques in the final analysis. There exists a chemical analog to cysteamine, phosphocysteamine, which is more palatable and demonstrates cystine depleting properties, although it has not been subjected to a rigorous clinical test of efficacy. The object of the study is to compare treatment with phosphocysteamine to cysteamine therapy in a randomized clinical trial. If some other drug with therapeutic promise is made available early enough in the study, then it, too, may be included in trial. Patient recruitment and treatment will be coordinated at a contracted study center at the University of California, San Diego. Data center functions will be performed at the University of Texas Health Science Center at Dallas. The study will encompass 3-4 years of enrollment and treatment of at least 80 patients. The drug will be evaluated on the basis of renal function as measured by serum creatinine levels and creatinine clearance, as a surrogate of glomerular filtration rate, at the end of the study.